Tasty Morsels of Critical Care

Welcome back to the tasty morsels of critical care podcast.

Following on from our initial post in this entirely accidental series on “things you don’t want to find in the chest drain” we turn our eyes (if not our noses) to empyema.

Many penumonias will develope a parapneumonic effusion. This is largely reactive and inflammatory but by no means does it mean there is infection. On the other hand parapneumonic effusions can become the seed for an empyema proper, something seen relatively commonly with something like strep pneumo.

The commonest bugs described in empyema are strep pneumo and staph aureus, both of which occur as complications of pneumonia with said bugs. If on the other hand you have perforated your oesophagus into your pleural space then expect to find a different selection of microbiological beasties.

While perhaps obvious, the clinical features we’ll be looking for are fever and pleural effusion either on CXR, CT or US. Fever despite appropriate antibiotics always should make us think about source control so if the CXR looks funny then put the probe on or run them through the CT scanner. You can see pleural enhancement on CT scans which in my somewhat limited experience seems quite specific but not especially sensitive. Similarly loculations can be very easily seen with ultrasound, better than CT it seems but again don’t necessarily correlate that well with empyema.

As such the best thing to do it seems is to get a sample. It is my contention that if you’re going so far as to get a sample then why not leave a little teeny weeny drain in there while you’re at it. The advent of US guidance and pig tails and a substantial literature base all suggest that small. bore drainage is actually often quite effective and the old days of just assuming everyone needs a 28fr drain are probably past. My own practice is to use an 8Fr pigtail and see what happens.

I have in my notes a list of fluid criteria that apparently define an empyema. I am unclear of the provenance of this list but it seems to have been drawn loosely from the 2017 thoracic surgery guidelines and some the intereventional trials we’ll talk about later.

So definitionally if we have pus it’s an empyema, if we have a positive gram stain it’s an empyema, if we have growth it’s an empyema. Other features suggestive on pleural fluid analysis include

• pH<7.2


• LDH>1000


• Sugar <2.2


• high lactate

So now let’s assume you’ve got your sample and you’ve tried small bore drainage and you still have a big collection there. What are your options?

Well, adding extra or bigger drains is all very reasonable and it would seem wise to involve a thoracic surgeon at some point. Unresolved these empyemas develop into what is known as the “rind” causing a trapped lung and many will need the rather brutal procedure of decortication to strip it away. However in the early days we’re likely to more interested in simply getting source control and sometimes it’s the loulcations that are our enemy.

There are a number of trials and indeed published guidelines suggesting the use of injected pleural therapies to aid drainage. This consists of 2 agents

1) DNAase

2) our old friend tPA

The intervention involves placing a small drain then injecting DNAase and tPA into the drain every 12 hrs. This has been moderately well studied with MIST-2 2011 and the Picollo trial (2014) being commonly quoted trials suggesting benefit. There is a cochrane review looking at tPA on its own that also suggests less need for surgery

The major downside, understandably is pleural bleeding, that occurs in about 2-5% in the studied cohorts. This can be clinically significant though very rarely does it seem to be life threatening.

The major barrier to implementation in the ICU setting is the almost complete absence of ICU patients from these trial cohorts. And as we all know if there is a complication possible it’s almost definitely going to happen with greater frequency in the ICU cohort.

I have not mentioned it so far, which is somewhat remiss of me, but if it’s not obvious you will also need some antibiotics here… To answer an SAQ with lots on definitions and drainage and fail to mention antibiotics would be poor form.

Reading

Deranged Physiology has this covered as always

– Piccolo, F. et al. Intrapleural Tissue Plasminogen Activator and Deoxyribonuclease for Pleural Infection. An Effective and Safe Alternative to Surgery. Ann. Am. Thorac. Soc. 11, 1419–1425 (2014).

– M., R. N. et al. Intrapleural Use of Tissue Plasminogen Activator and DNase in Pleural Infection. N. Engl. J. Med. 365, 518–526 (2011).

– Altmann, E. S., Crossingham, I., Wilson, S. & Davies, H. R. Intra‐pleural fibrinolytic therapy versus placebo, or a different fibrinolytic agent, in the treatment of adult parapneumonic effusions and empyema. Cochrane Database Syst.Rev. 2019, (2019).

– Shen, K. R. et al. The American Association for Thoracic Surgery consensus guidelines for the management of empyema. J. Thorac. Cardiovasc. Surg. 153, e129–e146 (2017).